Spiral crossflow filter

ABSTRACT

The present disclosure describes a spiral cross-flow filter. The spiral cross-flow filter includes a filter element having a continuous web of leaves formed by pleating a laminate filter element. The filter element may include a composite filter material including a first layer of a membrane material adjacent an outer shell, and a second layer of a permeate spacer material adjacent a permeate tube. The plurality of leaves wrap around the permeate tube in a uniform “spiral” configuration and may be separated by feed spacers.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation-in-part application, andclaims the benefit of the filing date under 35 U.S.C. §120, of U.S.patent application Ser. No. 12/586,770, filed on Sep. 28, 2009, andissued as U.S. Pat. No. 8,454,829 on Jun. 4, 2013. U.S. patentapplication Ser. No. 12/586,770 claims priority under 35 U.S.C. §119(e)to U.S. Provisional Patent Application No. 61/100,917, filed Sep. 29,2008. U.S. patent application Ser. Nos. 12/586,770 and 61/100,917 areincorporated by reference herein.

FIELD OF TECHNOLOGY

The present disclosure relates to improved spiral crossflow filters andmethods involving spiral crossflow filters.

BACKGROUND

Crossflow filtration is a type of membrane filtration that can be usedwhen a fluid carries an amount of solid material that could plug a “deadend” filter. Crossflow filtration is different from dead end filtration.In dead end filtration, the feed is passed through a membrane or bed,trapping the retentate in the membrane or bed, and releasing thefiltrate through the membrane or bed. Generally in dead end filtration,the only way for the feed fluid to exit the filter is through themembrane. In crossflow filtration, however, the feed is passed acrossthe filter membrane (tangentially to the filter membrane) at somepressure, concentration, or other differential between the feed and thefiltrate on the other side of the membrane. Material which is smallerthan the membrane pore size passes through the membrane as filtrate.Some of the feed is trapped in or on the membrane as retentate, whilethe remaining feed flow passes across the filter on the feed sidewithout passing through the membrane or becoming trapped in or on themembrane. The unfiltered feed flow exiting the filter is kept separatefrom the filtrate and may be recycled back through the filter. This modeof operation may be used for feeds with solids that cause a risk of“blinding.” Blinding is an accumulation of retentate on the membranethat fouls and/or reduces the effectiveness of a filter. With dead endfiltration, solid material can quickly blind the filter surface, andfeed flow can no longer pass through the membrane, rendering the filterineffective. With crossflow filtration, the tangential motion of thebulk of the fluid across the membrane causes trapped particles on thefilter surface to be removed by the tangential feed flow. This meansthat a crossflow filter can operate continuously with reduced blindingat a relatively high solids load compared to dead end filters.

Crossflow filter devices can take many shapes, including plates, hollowfibers, tubes and spirals. A spiral crossflow filtration device mayinclude filter media wrapped around a permeate tube in a “jelly roll”type design. When looking at the end of a “spiral” filter, the end edgesof the individual leaves of the filter element make a plane curve tracedby a point circling about the center axis but at ever-greater distancesfrom it. Each “leaf” is essentially hollow, like an “envelope” made outof filter media. In a spiral crossflow filter, the feed fluid flowsparallel to the permeate tube. The feed flow enters one of the leaf“envelopes” across the filter media. The filtered fluid, or permeate,goes through the media and spirals between the media inside the leaf“envelope” and into the permeate tube. The permeate exits the filterthrough the permeate tube, and is kept separate from the remaining feedflow which exits the filter separately.

Crossflow membrane filtration technology has been used widely inindustry globally. Cross flow filtration may be used, for example, inmicrofiltration, ultrafiltration, nanofiltration, and reverse osmosis.There is still a need, however, for improved cross-flow filter devices.

BRIEF SUMMARY

Embodiments described in the present disclosure include a spiralcross-flow filter including an outer cylindrical shell and a permeatecylindrical tube coaxially aligned within the shell and radially offsettherefrom. The filter may also include an annular pleated filter elementdisposed within an annulus between the outer shell and the permeatetube. The filter element may include a composite filter materialincluding a first layer of a membrane material adjacent the outer shell,and a second layer of a permeate spacer material adjacent the permeatetube. The pleats of the filter element may define a plurality ofcircumferentially spaced radial leaves, each including an attachment atits proximal edge to the permeate tube. The plurality of leaves may wraparound the permeate tube in a “spiral” configuration.

It is understood that the disclosed invention is not limited to theembodiments described in this Summary. The invention is intended toencompass modifications and other subject matter that are within thescope of the invention as defined solely by the claims.

BRIEF DESCRIPTION OF THE FIGURES

Various characteristics and features of the disclosed non-limitingembodiments may be better understood by reference to the followingfigures, in which:

FIG. 1 is a schematic exploded perspective view of an embodiment of aspiral cross-flow filter according to the present disclosure;

FIG. 2 is a schematic view of a membrane and permeate spacer materialthat make up a composite filter element of a cross-flow filter as shownin FIG. 1;

FIG. 3 is a schematic view of a composite sandwich of the materialsshown in FIG. 2, illustrated in a partially pleated configuration;

FIG. 4 is a schematic partial cross-sectional view of the crossflowfilter shown in FIG. 1, illustrating an edge of a pleated compositesandwich of a filter element attached to the permeate tube;

FIG. 5 is a schematic partial perspective view of the crossflow filtershown in FIG. 1, illustrating an edge of a pleated composite sandwich ofa filter element attached to the permeate tube;

FIG. 6 is a schematic partial perspective view of the crossflow filtershown in FIG. 1, illustrating an edge of a pleated composite sandwich ofa filter element attached to the permeate tube and having a feed spacer;

FIG. 7 is a schematic end view of an end cap of the cross-flow filtershown in FIG. 1;

FIG. 8 is a schematic sectional view taken along line “A-A” in FIG. 7and showing an end cap attached to a spiral filter;

FIG. 9 is a schematic cross-sectional side view of a permeate tubecomprising a blocked middle portion and radially offset perforatedsections forming annular manifolds disposed towards the inlet and outletends of the permeate tube;

FIG. 10 is a schematic partial perspective view of the permeate tubeshown in FIG. 9;

FIG. 11A is a schematic partial cross-sectional side view of the inletend of the permeate tube shown in FIG. 9; FIG. 11B is a schematicpartial cross-sectional side view of the outlet end of the permeate tubeshown in FIG. 9;

FIG. 12 is a schematic partial perspective view of the permeate tubeshown in FIG. 9 with a pleated filter element comprising a plurality ofcircumferentially spaced leaves attached to an outer cylindrical surfaceof the permeate tube adjacent to the annular manifold;

FIG. 13A is a schematic cross-sectional end view of the inlet portion ofa filter comprising the permeate tube shown in FIG. 9 co-axially alignedwith and radially offset from an outer cylindrical shell, and comprisingan annular pleated filter element comprising a plurality ofcircumferentially spaced leaves attached to an outer cylindrical surfaceof the permeate tube; FIG. 13B is a schematic cross-sectional end viewof the outlet portion of a filter comprising the permeate tube shown inFIG. 9 co-axially aligned with and radially offset from an outercylindrical shell, and comprising an annular pleated filter elementcomprising a plurality of circumferentially spaced leaves attached to anouter cylindrical surface of the permeate tube;

FIG. 14A is a schematic partial cross-sectional axial view of the inletportion of the permeate tube and filter element assembly shown in FIGS.9 and 13A and illustrating the attachment of the circumferentiallyspaced leaves to the permeate tube; FIG. 14B is a schematic partialcross-sectional axial view of the outlet portion of the permeate tubeand filter element assembly shown in FIGS. 9 and 13B and illustratingthe attachment of the circumferentially spaced leaves to the permeatetube;

FIG. 15 is a schematic partial cross-sectional side view of the inletportion of the permeate tube and filter element assembly shown in FIGS.9 and 13A illustrating tangential flow through the circumferentiallyspaced leaves; and

FIG. 16 is a schematic side view of the permeate tube and filter elementassembly shown in FIG. 9 illustrating tangential flow through thecircumferentially spaced leaves.

DETAILED DESCRIPTION

It is to be understood that the various descriptions of the embodimentsdisclosed herein have been simplified to illustrate only those elements,features, and aspects that are relevant to a clear understanding of thedisclosed embodiments, while eliminating, for purposes of clarity, otherelements, features, and aspects. Persons having ordinary skill in theart, upon considering the present description of the disclosedembodiments, will recognize that other elements and/or features may bedesirable in a particular implementation or application of the disclosedembodiments. However, because such other elements and/or features may bereadily ascertained and implemented by persons having ordinary skill inthe art upon considering the present description of the disclosedembodiments, and are therefore not necessary for a completeunderstanding of the disclosed embodiments, a description of suchelements and/or features is not provided herein. As such, it is to beunderstood that the description set forth herein is merely exemplary andillustrative of the disclosed embodiments and is not intended to limitthe scope of the invention as defined solely by the claims.

In the present disclosure, other than where otherwise indicated, allnumbers expressing quantities or characteristics are to be understood asbeing prefaced and modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, any numerical parametersset forth in the following description may vary depending on the desiredproperties one seeks to obtain in the embodiments according to thepresent disclosure. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of theclaims, each numerical parameter described in the present descriptionshould at least be construed in light of the number of reportedsignificant digits and by applying ordinary rounding techniques.

Also, any numerical range recited herein is intended to include allsub-ranges subsumed therein. For example, a range of “1 to 10” isintended to include all sub-ranges between (and including) the recitedminimum value of 1 and the recited maximum value of 10, that is, havinga minimum value equal to or greater than 1 and a maximum value of equalto or less than 10. Any maximum numerical limitation recited herein isintended to include all lower numerical limitations subsumed therein andany minimum numerical limitation recited herein is intended to includeall higher numerical limitations subsumed therein. Accordingly,Applicants reserve the right to amend the present disclosure, includingthe claims, to expressly recite any sub-range subsumed within the rangesexpressly recited herein. All such ranges are intended to be inherentlydisclosed herein such that amending to expressly recite any suchsub-ranges would comply with the requirements of 35 U.S.C. §112, firstparagraph, and 35 U.S.C. §132(a).

The grammatical articles “one”, “a”, “an”, and “the”, as used herein,are intended to include “at least one” or “one or more”, unlessotherwise indicated. Thus, the articles are used herein to refer to oneor more than one (i.e., to at least one) of the grammatical objects ofthe article. By way of example, “a component” means one or morecomponents, and thus, possibly, more than one component is contemplatedand may be employed or used in an implementation of the describedembodiments.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein, isincorporated herein in its entirety, but only to the extent that theincorporated material does not conflict with existing definitions,statements, or other disclosure material expressly set forth in thisdisclosure. As such, and to the extent necessary, the express disclosureas set forth herein supersedes any conflicting material incorporatedherein by reference. Any material, or portion thereof, that is said tobe incorporated by reference herein, but which conflicts with existingdefinitions, statements, or other disclosure material set forth hereinis only incorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

The present disclosure includes descriptions of various embodiments,including various different features, aspects, and characteristics ofthe embodiments. It is to be understood that all embodiments describedherein are exemplary, illustrative, and non-limiting. Thus, theinvention is not limited by the description of the various exemplary,illustrative, and non-limiting embodiments. Rather, the invention isdefined solely by the claims, which may be amended to recite anyfeatures, aspects, and characteristics expressly or inherently describedin or otherwise expressly or inherently supported by the presentdisclosure.

In addition, the figures presented herein represent non-limitingembodiments of the disclosure. The figures are not drawn to scale orproportion and are provided solely to aid in the understanding of thevarious embodiments, and should not be interpreted to limit the scope ofthe present disclosure.

The embodiments described herein generally relate to devices forremoving contaminants from a fluid, such as, for example, a liquid(e.g., water) or a gas (e.g., air). The embodiments described herein mayalso find utility in connection with other fluids. For example, a fluidto be purified or otherwise filtered may be any chemical, industrial, orbiological fluid. As generally used herein, “contaminant” may refer toany undesirable agent in a fluid. For example, “contaminants” mayinclude, but are not limited to, any solids and debris, heavy metals,polyaromatics, halogenated polyaromatics, minerals, vitamins,microorganisms or microbes (as well as reproductive forms ofmicroorganisms, including cysts and spores) including viruses, fungi(for example, molds and yeasts), proteins and nucleic acids, pesticidesand other agrochemicals including organic chemicals, inorganicchemicals, and dissolved salts.

As generally used herein, “removing contaminants” or “reducingcontaminants” refers to disarming or removing one or more contaminantsin the fluid, whether by physically or chemically removing, reducing,inactivating the contaminants, or otherwise rendering the one or morecontaminants harmless. In addition, the present disclosure furtherenvisions various aspects wherein particular embodiments includeremoving one or more contaminants but specifically excludes one or moretypes, groups, categories, or specifically identified contaminants aswell. For example, in various aspects, “removing contaminants” mayinclude one or more particular contaminants, or may include only oneparticular contaminant, or may specifically exclude one or morecontaminants.

FIG. 1 depicts an embodiment of a spiral cross-flow filter 1 accordingto various embodiments of the present disclosure. These embodiments havean outer cylindrical shell 3 and a porous permeate cylindrical tube 4coaxially aligned within the shell 3 and radially offset therefrom.These embodiments further have an annular pleated filter element 5disposed within an annulus 6 between the outer shell 3 and the permeatetube 4. The filter element 5 is formed from a plurality of leaves 7 anda plurality of feed spacers 8. For ease of illustration, the leaves 7and feed spacers 8 shown in FIG. 1 are not completely wrapped and packedtightly in “spiral” or “jelly-roll” configuration. Various embodimentsof the cross-flow filter 1 may include end caps 2.

Referring now to FIG. 2, a filter element may include a compositesandwich having at least a first layer of membrane material 9, and asecond layer of a permeate spacer material 10. In a spiral filter asillustrated in FIG. 1, the first layer of a membrane material 9 may beadjacent the outer shell 3, and the second layer of permeate spacermaterial 10 may be adjacent the permeate tube 4. Referring now to FIG.3, a composite sandwich filter element 5 may include both layers and maybe is pleated. A pleated filter element 5 may be placed around apermeate tube 4. Once placed around the permeate tube 4, the pleats ofthe filter element 5 may define a plurality of continuous,circumferentially spaced radial leaves 7. Once the filter element 5 isplaced around the permeate tube 4, the leaves 7 may be wrapped aroundthe permeate tube 4 in a uniform direction. The leaves 7 may bemaintained in the wrapped position by the outer shell 3, and/or the endcaps 2, for example. In various embodiments, the filter element 5 maynot be attached to the permeate tube 4. In various embodiments, eachleaf 7 may have an attachment 12 at its proximal edge 11 to the permeatetube 4. Once an attachment is formed, the plurality of leaves 7 may bewrapped around the permeate tube 4 in a uniform direction. FIG. 4 showsa partial cross-sectional view of a filter element 5 attached to apermeate tube 4. FIG. 4 shows only a portion of the permeate tube 4, andonly two of a plurality of leaves 7. The filter element 5 includesattachments 12 at the proximal edges 11. Once attached to the permeatetube 4, each leaf 7 can be described as a “hollow envelope,” having twolayers 9,10.

FIG. 6 shows two leaves 7 of a filter element 5 attached to a permeatetube 4. Though only two leaves 7 are shown, various embodiments may havea greater number of leaves 7 attached continuously around thecircumference of the permeate tube 4. In FIG. 6, the leaves 7 arepartially wrapped around the permeate tube 4 in the uniform directionshown by the arrow 13, but are not wrapped completely in the final“spiral” or “jelly roll” configuration. The filter element 5 shown inFIG. 6 further includes a feed spacer 8 inserted in between the twoleaves 7. In various embodiments, the filter element 5 includes a feedspacer 8 between each of the plurality of leaves 7. The purpose of thefeed spacer 8 is to maintain separation between the leaves 7 toestablish a feed flow path through the length of the filter element 5.The cross-flow facilitated by the feed spacers 8 helps to keep themembrane 9 from becoming fouled or blinded with aggregate retentate.

FIGS. 5 and 6 show partial perspective views of an end of a permeatetube 4 and filter element 5. In FIG. 5, the leaves 7 have not yet beenwrapped around the permeate tube 4. In FIG. 6, the leaves 7 arepartially wrapped around the permeate tube 4. Referring now to FIGS. 5and 6, in various embodiments, each of the plurality of leaves 7 has abond 14 at an edge 15 (inlet edge and/or an outlet edge), the bond 14sealing together membrane material 9 and the permeate spacer material10. As used herein, the term “seal” or “sealed” means that asubstantially fluid impervious seal is formed, but the materials are notnecessarily bonded together. As used herein, the term “bond” or “bonded”means that the materials described are physically and/or chemicallybonded together, for example, with an adhesive, or some bondingtechnique, such as, for example, ultrasonic welding, such that asubstantially fluid impervious seal is formed. The leaves 7 shown inFIGS. 5 and 6 also include an attachment 12 along proximal edge 11 ofthe leaves 7. Once bonded at the edges 15 and attached to the permeatetube 4, a “hollow envelope” having two layers is formed. The edge bond14 can be formed after pleating and before being attached to thepermeate tube 4, or after being attached to the permeate tube 4. Theedge 15 of each leaf 7 is bonded together, yet the proximal edges 11 areslightly separated where they form an attachment 12 to the permeate tube4. Therefore, in various embodiments, a small gap 16 may be formed nearthe proximal edges 11 of each leaf 7. In such embodiments, the gap 16may be covered and sealed by the inner portion 20 of an end cap 2. Invarious embodiments, the end cap 2 is bonded to a portion of each leaf7, covering and sealing the gap 16.

Referring now to FIG. 5, because the plurality of leaves 7 are formedfrom at least one pleated filter element 5, the leaves 7 are continuousexcept for where the ends 17 of the pleated filter element 5 meet. InFIG. 5, each end 17 of the filter element 5 makes up half of a leaf 7.Therefore, in various embodiments, at least one leaf 7 will have a bond18 at the distal edge 19, joining the two ends 17 of the pleated filterelement 5 and forming a leaf 7 with the ends 17. In various embodiments(not shown), each end 17 of the pleated filter element 5 will be the endof a complete leaf 7, and will not be a half of a leaf 7. In such anembodiment, the end 17 forms an attachment 12 at the proximal edge 11.The ends 17 of the filter element 5 will end in a complete leaf 7, andno leaf 7 will be formed by joining the ends 17 of a pleated filterelement 5.

In various embodiments, the bonds 14, 18 and the attachments 12 do notcomprise an adhesive. In various embodiments, the bonds 14, 18 and theattachments 12 are selected from the group consisting of an ultrasonicbond, a thermal bond, an IR bond, a radio frequency bond, and amicrowave bond. In various embodiments, the bonds 14, 18 and theattachments 12 are an ultrasonic bond. In various embodiments, theattachments 12 are an ultrasonic bond that bonds the membrane 9 materialand the permeate spacer 10 material of each leaf 7 at the proximal edge11 to the permeate tube 4. In various embodiments, the bonds 14, 18 areultrasonic bonds that bond the membrane 9 material and the permeatespacer 10 material of each leaf 7 at the edge 15 and a distal edge 19.In various embodiments, filter components that include an ultrasonicbond may be formed from the same base polymer, including any of thepolymers recited herein. In various embodiments, the components may beformed from base polymers that are compatible for the purpose ofultrasonic bonding or welding. These components include the membrane 9material, permeate spacer 10 material, permeate tube 4, end cap 2 andouter shell 3. These components may also include the feed spacer 8 andany other component described herein.

As shown in FIGS. 1 and 6, in various embodiments, the feed spacer 8 isformed from a corrugated thermoplastic sheet. The corrugations in thefeed spacer 8 establish flow channels that create less flow restrictionin the feed flow path compared to flat netting or other materials. Itwas surprisingly discovered that the use of a corrugated feed spacer 8helps to balance the flow across the filter 1 allowing the filter 1 tohandle higher cross flow rates, higher viscosity fluids, and higheramounts of feed solids while at the same time helping to avoid blinding.In various embodiments, the corrugated thermoplastic sheets forming thefeed spacers 8 are porous. As used herein, “porous” includes a range ofopenings from microscopic apertures to macroscopic apertures. In variousembodiments, the openings may be formed by an open lattice comprising anextruded thermoplastic net, for example. The openings may be formed insitu as the feed spacer 8 material is made, or the openings may becreated by mechanical or chemical methods (e.g., punching, boring,drilling, perforating, and the like) after the feed spacer 8 material ismade. In various embodiments, the corrugated thermoplastic sheetsforming the feed spacers 8 are non-porous and substantially fluidimpervious.

In various embodiments, the feed spacer 8 is formed from a corrugatedthermoplastic sheet that is non-textured. As used herein, the term“non-textured” includes a surface that is substantially smooth on amacroscopic level. In various embodiments, the corrugated thermoplasticsheet is textured. As used herein, the term “textured” includes asurface that has raised features visible on a macroscopic level. Atextured sheet may help to create turbulence in the fluid flow which mayaid in the operation of the spiral crossflow filter as described herein.Examples of corrugated feed spacers may be found in U.S. Pat. No.4,834,881 to Sawada et al., incorporated by reference herein.

In various embodiments, the corrugated thermoplastic sheet has anamplitude from 0.02 inches to 0.25 inches, and a wavelength from 0.02inches to 0.25 inches. In various other embodiments, the corrugatedthermoplastic sheet has an amplitude from 0.05 inches to 0.15 inches,and a wavelength from 0.05 inches to 0.15 inches. In variousembodiments, the feed spacer 8 is made from a thermoplastic selectedfrom the group consisting of polyvinylidene fluoride, polypropylene,polyester, polyethylene, polyethersulfone, polysulfone,polyacrylonitrile, nylon, ethylene chlorotrifluoroethlyene,fluoroethylenepropylene, perfluoroalkoxy, polyetheretherketone,polysynidilenesulfide, polycarbonate, and co-polymers and blends of anythereof.

FIG. 7 shows an end view of an end cap 2. Various embodiments mayinclude an inlet end cap 2 on an inlet end of the permeate tube 4, andan outlet end cap 2 on an outlet end of the permeate tube 4. The endcaps 2 have an inner portion 20 sealing the inlet end or outlet end ofthe permeate tube 4. In various embodiments, the inner portion 20 alsoseals gaps 16 near the proximal edges 11 of the leaves 7, and may bebonded to a portion of the leaves 7. The end cap 2 also has at least oneopen portion 21 directing the inlet fluid flow towards inlet edges 15 ofthe plurality of leaves 7, or directing an outlet fluid flow from theoutlet edges 15 of the plurality of leaves 7. Various embodiments mayinclude an outlet end cap 2 attached to at least an outlet end of thepermeate tube 4, the outlet end cap 2 having structures configured toseparate the permeate fluid flow flowing from the permeate tube 4 fromthe outlet fluid flow flowing from the outlet edges 15 of the pluralityof leaves 7.

Referring now to FIG. 8, in various embodiments, the end cap 2 is bondedto and seals the end of the permeate tube 4. In various embodiments, onthe inlet side, the inner portion 20 of the end cap 2 is closed, suchthat no fluid enters the permeate tube 4 at the inlet end. On the outletside, the inner portion 20 of the end cap 2 is open, such that permeatemay exit the filter 1. In various embodiments, both the inlet and outletends of the permeate tube 4 are open, and not blocked by the innerportion 20 of the end caps 2. In various embodiments, a middle portionof the permeate tube 4 is blocked. In such an embodiment, fluid flows inthe inlet end of the permeate tube 4. The blocked middle portion forcesthe fluid out of the permeate tube and into the leaves 7. Once in theleaves, the fluid flows parallel to the permeate tube 4 and remains inthe leaves. In such an embodiment, the filtered fluid can pass from feedside to permeate side or from permeate side to feed side. The fluidre-enters the permeate tube 4 downstream from the blocked middle portionof the permeate tube. In various other embodiments, both ends of thepermeate tube 4 are open and both ends are outlet ends. This allows fora reduced fluid flow restriction since fluid crossing the membrane 9 andentering the leaves 7 and then the permeate tube 4 may exit the permeatetube 4 at either end.

In FIG. 8, the filter element 5 is indicated by the shaded area. Aplurality of leaves 7 are wrapped around the permeate tube 4 in auniform direction, however, individual leaves 7 are not shown in thisfigure. In embodiments as illustrated in FIG. 8, the ribs 22 of the endcap 2 are not bonded to the edges 15 of the leaves 7. In variousembodiments, the ribs 22 are bonded to the edges 15 of the plurality ofleaves 7 of the filter element 5. As previously mentioned, the innerportion 20 of the end cap 2 may also seal or be bonded to a portion ofthe leaves 7 that may include a gap 16.

The outer cylindrical shell 3 may be made of a rigid thermoplastic,fiberglass, or metal tube, or may be made of a non-rigid material, suchas, for example, but not limited to, tape. In various embodiments, theouter cylindrical shell 3 may be formed after the leaves 7 have beenwrapped around the permeate tube 4. In such embodiments, the shell 3 maybe formed by wrapping a flexible material such as fiberglass around thefilter element 5. In either case, the outer portion 23 of the end cap 2forms a seal with the outer cylindrical shell 3. In various embodiments,the outer portion 23 of the end cap 2 may further be bonded to the shell3. In various embodiments, the inlet end cap 2 and outlet end cap 2 arebonded to at least the permeate tube 4, and possibly also the shell 3,by a method selected from the group consisting of ultrasonic welding,thermal bonding, IR bonding, radio frequency bonding, and microwavebonding.

In operation, feed flow is directed at the inlet edges 15 of the leaves7 of the filter element 5. The feed flow may enter the spiral filter 1through openings 21 in the end cap 2. Feed flow is directed in betweenthe leaves 7 at the inlet edges 15. Space may be maintained in betweenthe leaves 7 by feed spacers 8. Filtrate may pass through the membrane 9and enter the leaf 7 at any point along any of the leaves 7 that arewrapped around the permeate tube 4. The filtrate may be forced throughthe membrane 9 by a pressure differential, concentration gradient, orany other means. Once filtrate has passed through the membrane 9 of aleaf 7, the filtrate remains within that leaf 7. The filtrate is forcedto flow towards the permeate tube 4 while inside of the leaf 7. Whileinside of the leaf 7, the filtrate must eventually pass through thepermeate spacer 10 so that it can enter the porous permeate tube 4. Thepermeate tube 4 is porous for at least a portion of its length such thatit is in fluid communication with the inside of each leaf 7. Once insidethe permeate tube 4, the filtrate flows out of the filter 1 through theoutlet end of the permeate tube 4. The filtrate is kept separate fromfeed flow exiting the filter 1 that has not entered a leaf 7. Feed flowthat has not entered a leaf 7 exits the spiral filter 1 past the outletedges 15 of the leaves 7 of the filter element 5. A constant stream ofunfiltered feed flowing tangentially to the leaves 7 helps to remove orcarry away retentate from the filter surface membrane 9 and keeps themembrane 9 from blinding. In various embodiments, the remaining feedflow exits the filter 1 through openings 21 in an outlet end cap 2. Theunfiltered feed flow may eventually be recycled back into the spiralfilter 1 through the inlet end cap 2.

In various embodiments, a filter as described herein may have across-flow rate (measured as fluid velocity) of greater than or equal to3 M/sec. In various embodiments, a filter as described herein may have across-flow rate of greater than or equal to 5 M/sec. In variousembodiments, a filter as described herein may have a cross-flow rate ofless than or equal to 1 M/sec. In various embodiments, a filter asdescribed herein may have a cross-flow rate from 1 M/sec to 5 M/sec orfrom 1 M/sec to 3 M/sec. In various other embodiments, a filter asdescribed herein may have a cross-flow rate from 20 cm/sec to 100cm/sec.

In various embodiments, a cross-flow filter as described herein may havea ratio of leaf height to spiral diameter of less than or equal to 3, insome embodiments less than or equal to 2.5, and in other embodimentsless than or equal to 2. As used herein, “leaf height” refers to thedistance from a point between the proximal edges of a leaf to the distaledge of a leaf when the leaf extends radially from a permeate tube, forexample, as shown in FIGS. 4 and 5. As used herein, “spiral diameter”refers to the length of the diameter of a filter as described herein,measured from the outside edge of the permeate tube to the inside edgeof the outer cylindrical shell.

A filter as described herein may be used for a variety of filteringapplications. In various embodiments, the membrane material of a spiralcrossflow filter may be made from a material selected from the groupconsisting of a microfiltration material, an ultrafiltration material, ananofiltration material, and a reverse osmosis material. As used herein,a microfiltration material is defined as a porous filter material thatremoves the majority of particles less than 10 microns down to 0.01microns, typically at a greater than 90% efficiency. An ultrafiltrationmaterial, as used herein, is defined as a porous filter material that,in addition to performing like a microfiltration material, removes themajority of molecules from about 1 million Daltons down to less than1,000 Daltons, typically at a greater than 90% efficiency. As usedherein, a nanofiltration material is defined as a porous filter materialthat, in addition to performing as an ultrafiltration material, removesthe majority of multi-valent ions, typically at a greater than 90%efficiency. As used herein, a reverse osmosis material is defined as aporous filter material that, in addition to performing as ananofiltration material, removes the majority of single valent ions,typically at a greater than 90% efficiency.

A filter as described herein may be useful with any known materialsuitable for the types of filtration listed herein. In variousembodiments, a membrane material may be selected the group consisting ofa microfiltration material and an ultrafiltration material. In variousembodiments, the membrane material may be formed from a materialselected from the group consisting of polyvinylidene fluoride,polypropylene, polyester, polyethylene, polyethersulfone, polysulfone,polyacrylonitrile, nylon, ethylene chlorotrifluoroethlyene,fluoroethylenepropylene, perfluoroalkoxy, polytetrafluorethylene,polyetheretherketone, polysynidilenesulfide, and polycarbonate. Invarious embodiments, the membrane material may be selected from thegroup consisting of polyvinylidene fluoride and polyethersulfone.

Referring to FIGS. 9-11B, a permeate tube 104 comprises a middle portion140 separating an inlet portion 120 and an outlet portion 130. Themiddle portion 140 of the permeate tube 104 is blocked and does notpermit fluid flow through the entire length of the permeate tube 104.Instead, the blocked middle portion 140 forces fluid entering throughthe inlet end 125 of the permeate tube 104 out through perforation 155formed in an a radially offset section 153 of the inlet portion 120.Referring to FIG. 11A, fluid entering through the inlet end 125 of thepermeate tube 104 is depicted by arrow 160. The fluid flow 160 entersinto the hollow lumen 157 in the inlet portion 120 of the permeate tube104 and is forced out through perforations 155 in the radially offsetsection 153 of the cylindrical wall of the inlet portion 120, asdepicted by arrows 165.

The fluid flow 165 forced out of the inlet portion 120 of the permeatetube 104 enters the circumferentially spaced leaves of an annularpleated filter element (described in greater detail below in connectionwith FIGS. 12-16). Once in the leaves of the filter element, the fluidflows tangentially to the blocked middle portion 140 of the permeatetube 104 (see FIGS. 15 and 16, described below). Referring to FIG. 11B,after flowing tangentially through the leaves of the filter element, thefluid re-enters the permeate tube through perforations 155 in a radiallyoffset section 153 of the cylindrical wall of the outlet portion 130, asdepicted by arrows 175. The fluid flow 175 entering into the outletportion 130 of the permeate tube 104 through the perforations 155combines in the hollow lumen 157 in the outlet portion 130 and exits thepermeate tube 104 through outlet end 135, as depicted by arrow 170.

The inlet portion 120 and the outlet portion 130 of the permeate tube104 each comprise annular shaped manifolds 150 formed by the radiallyoffset sections 153 of the inlet portion 120 and the outlet portion 130.The radially offset sections 153 of the inlet portion 120 and the outletportion 130 are radially offset relative to the outer cylindricalsurface 147 of the middle portion 140. The radially offset sections 153of the inlet portion 120 and the outlet portion 130 are also radiallyoffset relative to the outer cylindrical surface 127 of the inletportion 120 and the outer cylindrical surface 137 of the outlet portion130, respectively. The radially offset sections 153 are radially offsetinwardly away from the outer cylindrical surfaces of the permeate tube104 and toward the hollow lumens 157 of the inlet portion 120 and theoutlet portion 130.

The perforations 155 in the cylindrical walls of the inlet portion 120and the outlet portion 130 of the permeate tube 104 are located in theradially offset sections 153 and form apertures that provide fluidcommunication between the manifolds 150 and the hollow lumens 157 in theinlet portion 120 and the outlet portion 130, respectively. Theperforated radially offset sections 153 of the cylindrical walls of theinlet portion 120 and the outlet portion 130 of the permeate tube 104divide the outer cylindrical surface of the permeate tube 104 into theouter cylindrical surface 127 of the inlet portion 120, the outercylindrical surface 137 of the outlet portion 130, and the outercylindrical surface 147 of the middle portion 140.

In the embodiment shown in FIGS. 9-11A, the permeate tube 104 has aconstant outer diameter along the entire axial length of the permeatetube other than at the radially offset sections 153 and at thetransitions from the outer cylindrical surfaces (127, 137, 147) of thepermeate tube 104 to the radially offset sections 153. However, it isunderstood that, in various embodiments, the outer diameter of apermeate tube may vary along the axial length of the permeate tube. Forexample, in various embodiments, the outer cylindrical surfaces 127 and137 of the inlet portion 120 and the outlet portion 130, respectively,may have a diameter that is less than or greater than the diameter ofthe outer cylindrical surface 147 of the middle portion 140. In variousembodiments, the perforated radially offset sections 153 may be radiallyoffset inwardly relative to at least one of the outer cylindricalsurface 127 of the inlet portion 120, the outer cylindrical surface 137of the outlet portion 130, and the outer cylindrical surface 147 of themiddle portion 140.

The middle portion 140 is located in between the radially offset section153 of the inlet portion 120 and the radially offset section 153 of theoutlet portion 130. In the embodiment shown in FIGS. 9-11B, the middleportion 140 of the permeate tube 104 is blocked along the entire axiallength of the middle portion 140 located between the respective radiallyoffset sections 153. However, it is understood that, in variousembodiments, a middle portion of a permeate tube may be blocked alongonly one or more sections of the axial length of the middle portion,provided that the middle portion blocks fluid flow through the permeatetube and forces fluid flow from an inlet portion through perforations ina radially offset section and into a manifold, and provided that fluidflow can re-enter an outlet portion of the permeate tube downstream fromthe middle portion through a manifold formed by a perforated radiallyoffset section of the outlet portion.

In the embodiment shown in FIGS. 9-11B, the permeate tube 104 issymmetrical about a midpoint along the axial length of the permeatetube. As such, the structural configuration and dimensions of the inletportion 120 and the outlet portion 130 are the same, including theperforated radially offset sections 153 and the manifolds 150. However,it is understood that, in various embodiments, the structuralconfiguration of the inlet portion 120 and the outlet portion 130 may bedifferent, provided that at least the inlet portion comprises aperforated radially offset section forming a manifold in fluidcommunication with a hollow lumen that opens to and provides fluidcommunication through the inlet end of the permeate tube.

For example, in various embodiments, the axial length of the radiallyoffset section of the inlet portion may be the same or different thanthe axial length of the radially offset section of the outlet portion;the magnitude of the radial offset of the radially offset section of theinlet portion may be the same or different than the magnitude of theradial offset of the radially offset section of the outlet portion; thenumber, shape, and/or dimensions of the perforations in the radiallyoffset section of the inlet portion may be the same or different thanthe number, shape, and/or dimensions of the perforations in the radiallyoffset section of the outlet portion; the inner diameter and/or axiallength of the hollow lumen of the inlet portion may be the same ordifferent than the inner diameter and/or axial length of the hollowlumen of the outlet portion; and/or the outer diameter and/or axiallength of the outer cylindrical surface of the inlet portion may be thesame and/or different than the outer diameter and/or axial length of theouter cylindrical surface of the outlet portion. In other embodiments,the inlet portion of a permeate tube may comprise a radially offsetsection and annular manifold and the outlet portion may lack a radiallyoffset section and annular manifold.

FIG. 12 illustrates an assembly comprising the permeate tube 104 shownin FIGS. 9-11A and a pleated filter element 105. The pleated filterelement 105 comprises a plurality of circumferentially spaced leaves 107defined by the pleats of the filter element 105. The filter element 105and the filter leaves 107 may, in various embodiments, comprise the samestructural configurations, materials of construction, sealing/bonding,and attachment mechanisms described above in connection with filterelement 5 and filter leaves 7 shown in FIGS. 1-6. The filter element 105is attached to the permeate tube 104 through attachments 112 formedbetween proximal edges 111 of the leaves 107 and the outer cylindricalsurfaces (127, 137, and/or 147) of the permeate tube 104 (see FIGs.14Aand 14B). For ease of illustration, the filter element 105 and leaves107 depicted in FIGS. 12-16 are shown in a spaced-apart configurationand lacking feed spacers positioned between adjacent leaves. However, itis understood that, in various embodiments, a filter may comprise apermeate tube and filter element assembly wherein the leaves of thefilter element are wrapped around the permeate tube in a uniformdirection in a final spiral or “jelly roll” type configuration. It isalso understood that, in various embodiments, a filter may comprise apermeate tube and filter element assembly comprising one or more feedspacers positioned between two or more adjacent leaves of the filterelement. Such feed spacers may comprise the same structuralconfigurations, materials of construction, and other features describedabove in connection with feed spacers 8 shown in FIGS. 1 and 6.

The leaves 107 of the filter element 105 comprise an axial length thatis substantially the same as the axial length of the permeate tube 104(see FIG. 16). The proximal edges 111 of the leaves 107 are in physicalcontact with and attached to the outer cylindrical surface 127 of theinlet portion 120. The proximal edges 111 of the leaves 107 are inphysical contact with and attached to the outer cylindrical surface 137of the outlet portion 130. The proximal edges 111 of the leaves 107 maybe, but are not necessarily, in physical contact with and attached tothe outer cylindrical surface 147 of the middle portion 140.

The attachments 112 between the proximal edges 111 of the leaves 107 andthe outer cylindrical surfaces of the permeate tube may be located alongthe entire axial lengths of the respective outer cylindrical surfaces ormay be located along only a segment of the axial lengths of therespective outer cylindrical surfaces or at discrete locations along theaxial lengths of the respective outer cylindrical surfaces such as, forexample, proximally and distally adjacent to the manifolds 150. Theattachments 112 between the proximal edges 111 of the leaves 107 and theouter cylindrical surfaces of the permeate tube may comprise chemical orphysical bonds that provide a substantially fluid impervious sealbetween the proximal edges 111 of the leaves 107 and at least a portionof an outer cylindrical surface of the permeate tube. For example,ultrasonic welding may be used to form bonds between the proximal edges111 of the leaves 107 and at least a portion of an outer cylindricalsurface of the permeate tube, for example, adjacent to a manifold.

A number of leaves 107 are omitted from the views shown in FIGS. 12,14A, 14B, 15, and 16 to illustrate the orientation of the filter element105 relative to the manifold 150. The circumferential spacing of theleaves 107 around the circumference of the permeate tube 104 (see FIGS.13A and 13B), and the attachment of the proximal edges 111 of the leaves107 to at least the outer cylindrical surface 127 of the inlet portion120 and the outer cylindrical surface 137 of the outlet portion 130 (seeFIGS. 14A and 14B), complete the annular configuration of the manifolds150, which completely encircle the perforated radially offset sections153 of the inlet portion 120 and the outlet portion 130 of the permeatetube. In this manner, the leaves 107 of the filter element 105 axiallyspan between the outer cylindrical surface 147 of the middle portion 140and the outer cylindrical surfaces 127 and 137 of the inlet and outletportions 120 and 130, respectively, but the leaves 107 do not enter intothe annular manifold 150 and, therefore, do not physically contact theperforated radially offset section 153.

The assembly comprising the permeate tube 104 and the pleated filterelement 105 may be positioned inside an outer cylindrical shell 103, asshown in FIGS. 13A and 13B, to form a spiral cross flow filter 101. Thepermeate tube 104 may be positioned in co-axial alignment with the outercylindrical shell 103 and radially offset therefrom, for example, in aconcentric orientation. The outer cylindrical shell 103 of the spiralcross flow filter 101 may comprise the same structural configurations,materials of construction, and other features described above inconnection with the outer cylindrical shell 3 of the spiral cross flowfilter 1 shown in FIGS. 1 and 8. In various embodiments, the spiralcross flow filter 101 may comprise an inlet end cap and an outlet endcap. For example, an inlet end cap and an outlet end cap may comprisethe same structural configurations, materials of construction, and otherfeatures described above in connection with the end cap 2 shown in FIGS.1, 7, and 8.

As illustrated in FIGS. 13A and 14A, fluid flow entering into the hollowlumen 157 in the inlet portion 120 of the permeate tube 104 and isforced out through perforations 155 in the radially offset section 153of the cylindrical wall of the inlet portion 120, as depicted by arrows165. The fluid flow 165 exits from the hollow lumen 157 of the inletportion 120 of the permeate tube and enters into the annular manifold150, which provides for a uniform distribution of the fluid flow fromthe inlet portion 120 of the permeate tube 104 to the internal envelope180 formed in the leaves 107 of the filter element 105. Once in theinternal envelope 180 in the leaves 107 of the filter element 105, thefluid flows tangentially to the blocked middle portion 140 of thepermeate tube, as depicted by arrows 190 in FIGS. 15 and 16. Thecomposite sandwich structure of the pleated filter element 105comprising membrane material 109 and permeate spacer material 110provides a semi-permeable barrier between the tangential permeatetube-side fluid flow 190 and a tangential shell-side fluid flow (notshown).

As illustrated in FIGS. 13B, 14B, and 16, the tangential fluid flow 190exits from the internal envelope 180 in the leaves 107 of the filterelement 105 and enters into the manifold 150, which provides for auniform distribution of the fluid flow from the filter element 105 tothe outlet portion 130 of the permeate tube 104, as depicted by arrows175. In this manner, the fluid flow 175 re-enters the permeate tube 104through perforations 155 in the radially offset section 153 of thecylindrical wall of the outlet portion 130. The fluid flow 175 enteringinto the outlet portion 130 of the permeate tube 104 through theperforations 155 combines in the hollow lumen 157 in the outlet portion130 and exits the permeate tube 104 through outlet end 135, as depictedby arrow 170.

Referring to FIGS. 14A and 14B, the pleats of the pleated filter element105 form the leaves 107, which may be wrapped around the permeate tube104 in a final spiral configuration in a cross-flow filter (not shown).The filter element 105 comprises a composite sandwich structurecomprising a first layer of membrane material 109 and a second layer ofpermeate spacer material 110. In a spiral wound cross-flow filter, thelayer of membrane material 109 may be located adjacent to an outer shell(not shown in FIGS. 14A and 14B, but see FIGS. 13A and 13B) and thelayer of permeate spacer material 110 may be located adjacent to thepermeate tube 104.

As shown in FIGS. 14A and 14B, both the layer of membrane material 109and the layer of permeate spacer material 110 are pleated to form theleaves 107 of the filter element 105. The leaves have proximal edges 111(proximal relative to the permeate tube 104), which physically contactat least the outer cylindrical surface 127 of the inlet portion 120 andthe outer cylindrical surface 137 of the outlet portion 130. The filterelement 105 is secured to the permeate tube 104 with attachments 112between at least a portion of the proximal edges 111 of the leaves 107and at least a portion of the outer cylindrical surface 127 of the inletportion 120 and the outer cylindrical surface 137 of the outlet portion130. In some embodiments, attachments 112 may also be formed between theproximal edges 111 of the leaves 107 and at least a portion of the outercylindrical surface 147 of the middle portion 140. The attachments 112,which may comprise, for example, ultrasonic welded bonds or anotheradhesive-free bonding mechanism, may be located along the entire axiallengths of the respective outer cylindrical surfaces or may be locatedalong only a segment of the axial lengths of the respective outercylindrical surfaces or at discrete locations along the axial lengths ofthe respective outer cylindrical surfaces. For example, the attachments12 may be located proximally and/or distally adjacent to the manifolds150 (proximal and/or distal relative to the axial length of the permeatetube 104). The attachments 112 secure the filter element 105 to thepermeate tube and maintain the internal envelopes 180 within each leaf107.

In various embodiments, the attachments and bonds described herein inconnection with the various components of a filter may be formed, forexample, by one or more of ultrasonic welding, thermal bonding, IRbonding, radio frequency bonding, microwave bonding, laser welding, orhot air welding.

Spiral cross-flow filters comprising permeate tubes comprising inlet andoutlet end manifolds facilitate filtration operations (e.g., membranedistillation and osmotic membrane distillation) that may benefit fromco-current or counter-current tangential flow through the filters (i.e.,tangential flow on both sides of the filtration membrane: permeatetube-side and shell-side). The annular manifolds described in thisspecification provide for optimized fluid flow dynamics by minimizingflow restrictions and producing a uniform distribution of fluid flowthrough the leaves of the filter element on the permeate tube-side ofthe pleated filter element.

An example of an application of spiral cross-flow filters comprisingpermeate tubes comprising inlet and outlet end manifolds is membranedistillation of brine (sodium chloride) or other salt-containing aqueoussolutions. A concentrated caustic solution (NaOH) flows through thepermeate tube-side of a spiral cross-flow filter comprising inlet andoutlet end manifolds, which facilitate the flow of the caustic solutionfrom the inlet of the permeate tube through the leaves of the filterelement and the outlet of the permeate tube. A brine solution flowsthrough the shell-side of the spiral cross-flow filter. The caustic andbrine solutions flowing through the filter are separated by ahydrophobic membrane material (e.g., polytetrafluoroethylene) comprisingthe filter element. The caustic and brine solutions flowing through thefilter are heated to a temperature less than the boiling pointtemperature of pure water, for example, about 90° C. Due to thedifference in the water vapor pressure of brine and caustic solutions(P_(v)(brine)>P_(v)(caustic)), water vapor transports through themembrane from the brine solution to the caustic solution, therebyconcentrating the brine solution and diluting the caustic solution.

The feed solutions to the spiral cross-flow filter may comprise wastestreams from a chemical plant and the exit streams from the spiralcross-flow filter may be recycled back to the chemical plant. In thismanner, membrane distillation using spiral cross-flow filters asdescribed in this specification may reduce waste discharges and feedrequirements for chemical processing operations. However, to optimizemembrane distillation of brine or other salt solutions, the thermalpolarization and chemical concentration polarization (i.e., localizedtemperature and concentration increases in a boundary layer immediatelyadjacent to the filtration membrane) need to be minimized. Chemicalconcentration polarization on the salt side may cause the formation ofsalt crystals on the membrane material, which can lead to wetting out ofthe hydrophobic material and cross-contamination. Chemical concentrationpolarization on the caustic side may decrease the water vaportransmission rate. Thermal polarization on either side may also decreasethe water vapor transmission rate. Therefore, it is important tomaintain a balanced tangential flow through the spiral cross-flow filteron both the permeate tube-side and the shell-side.

On the shell-side, the balanced tangential flow of salt solution betweenadjacent leaves of the filter element is generally not problematicbecause the salt solution can be fed to and withdrawn from the filterthrough ports in the outer shell or end caps. On the tube-side, however,the tangential flow of caustic solution within the leaves may beproblematic because the solution must flow from the permeate tube inletinto the leaves, out of the leaves, back into the permeate tube, andwithdrawn through the permeate tube outlet. The use of spiral cross-flowfilters comprising permeate tubes comprising inlet and/or outlet endmanifolds improves the distribution of flow through the leaves of thefilter element, thereby improving the flow dynamics and providing forthe balanced flow necessary to reduce polarization in membranedistillation operations.

In various embodiments, a spiral cross-flow filter may comprise an outershell, a permeate tube coaxially aligned within the outer shell andradially offset therefrom, and a pleated filter element located withinan annulus between the outer shell and the permeate tube. The filterelement may comprise a composite filter material. The composite filtermaterial may comprise a first layer of a membrane material adjacent theouter shell and a second layer of a permeate spacer material adjacentthe permeate tube. The pleats of the filter element may define aplurality of circumferentially spaced leaves. The plurality of leavesmay wrap around the permeate tube in a uniform direction. A middleportion of the permeate tube may be blocked and configured to directfluid out of the permeate tube, into the plurality of leaves, and backinto the permeate tube downstream from the blocked middle portion of thepermeate tube.

In various embodiments, a permeate tube may comprise at least onemanifold formed by a perforated radially offset section of a cylindricalwall of the permeate tube. One or more leaves of the plurality of leavesof the filter element may be attached to the permeate tube throughattachments between edges of the leaves and an outer cylindrical surfaceof the permeate tube adjacent to the manifold.

In various embodiments, a permeate tube may comprise a first manifoldpositioned adjacent to an inlet end of the permeate tube and a secondmanifold positioned adjacent to an outlet end of the permeate tube. Thefirst manifold may be formed by a perforated radially offset section ofa cylindrical wall of a hollow inlet portion of the permeate tube. Thesecond manifold may be formed by a perforated radially offset section ofa cylindrical wall of a hollow outlet portion of the permeate tube. Oneor more leaves of the plurality of leaves of the filter element may beattached to the permeate tube through attachments between edges of theleaves and an outer cylindrical surface of the inlet portion of thepermeate tube adjacent to the first manifold. One or more leaves of theplurality of leaves of the filter element may be attached to thepermeate tube through attachments between edges of the leaves and anouter cylindrical surface of the outlet portion of the permeate tubeadjacent to the second manifold.

In various embodiments, a spiral cross-flow filter comprises an outershell, a permeate tube coaxially aligned within the outer shell andradially offset therefrom, and a pleated filter element located withinan annulus between the outer shell and the permeate tube. The permeatetube may comprise a blocked middle portion, a hollow inlet portioncomprising a first manifold formed by a perforated radially offsetsection of a cylindrical wall of the inlet portion, and a hollow outletportion comprising a second manifold formed by a perforated radiallyoffset section of a cylindrical wall of the outlet portion. The filterelement may comprise a first layer of a membrane material adjacent theouter shell and a second layer of a permeate spacer material adjacentthe permeate tube. The pleats of the filter element may define aplurality of circumferentially spaced leaves, and the plurality ofleaves may wrap around the permeate tube in a uniform direction.

In various embodiments, a permeate tube comprises a blocked middleportion, a hollow inlet portion comprising a manifold formed by aperforated radially offset section of a cylindrical wall of the inletportion, and a hollow outlet portion. The hollow outlet portion may alsocomprise a manifold formed by a perforated radially offset section of acylindrical wall of the outlet portion.

The present disclosure has been written with reference to variousexemplary, illustrative, and non-limiting embodiments. However, it willbe recognized by persons having ordinary skill in the art that varioussubstitutions, modifications or combinations of any of the disclosedembodiments (or portions thereof) may be made without departing from thescope of the invention as defined solely by the claims. Thus, it iscontemplated and understood that the present disclosure embracesadditional embodiments not expressly set forth herein. Such embodimentsmay be obtained, for example, by combining, modifying, or reorganizingany of the disclosed steps, ingredients, constituents, components,elements, features, aspects, and the like, of the embodiments describedherein. Thus, this disclosure is not limited by the description of thevarious exemplary, illustrative, and non-limiting embodiments, butrather solely by the claims. In this manner, Applicants reserve theright to amend the claims during prosecution to add features asvariously described herein.

What is claimed is:
 1. A spiral cross-flow filter, comprising: an outershell; a permeate tube coaxially aligned within the outer shell andradially offset therefrom; and a pleated filter element comprisingpleats located within an annulus between the outer shell and thepermeate tube, the filter element comprising a composite filter materialcomprising: a first layer of a membrane material adjacent the outershell, and a second layer of a permeate spacer material adjacent thepermeate tube, the pleats of the filter element defining a plurality ofcircumferentially spaced leaves, wherein the plurality of leaves wraparound the permeate tube in a uniform direction, wherein each leafcomprises an attachment to the permeate tube at a proximal edge of theleaf, and wherein each attachment comprises a direct bond between thepermeate tube and the membrane material; wherein a middle portion of thepermeate tube is blocked and configured to direct fluid out of thepermeate tube, into the plurality of leaves, and back into the permeatetube downstream from the blocked middle portion of the permeate tube. 2.The filter of claim 1, wherein the permeate tube comprises at least onemanifold formed by a perforated section of a cylindrical wall of thepermeate tube, which is radially offset inwardly away from an outercylindrical surface of the middle portion of the permeate tube, andwhich is radially offset inwardly away from an outer cylindrical surfaceof an inlet portion or an outlet portion of the permeate tube.
 3. Thefilter of claim 2, wherein one or more leaves of the plurality of leavesof the filter element are attached to the permeate tube throughattachments between edges of the leaves and an outer cylindrical surfaceof the permeate tube adjacent to the manifold.
 4. The filter of claim 3,wherein the attachments do not comprise an adhesive.
 5. The filter ofclaim 3, wherein the attachments comprise a bond between the edges ofthe leaves and an outer cylindrical surface of the permeate tubeadjacent to the manifold, the bond formed by ultrasonic welding, thermalbonding, IR bonding, radio frequency bonding, microwave bonding, laserwelding, or hot air welding.
 6. The filter of claim 1, wherein thepermeate tube comprises: a first manifold positioned adjacent to aninlet end of the permeate tube; and a second manifold positionedadjacent to an outlet end of the permeate tube; wherein the firstmanifold is formed by a perforated section of a cylindrical wall of ahollow inlet portion of the permeate tube, wherein the perforatedsection is radially offset inwardly away from an outer cylindricalsurface of the middle portion of the permeate tube, and is radiallyoffset inwardly away from an outer cylindrical surface of the hollowinlet portion of the permeate tube; and wherein the second manifold isformed by a perforated section of a cylindrical wall of a hollow outletportion of the permeate tube, wherein the perforated section is radiallyoffset inwardly away from an outer cylindrical surface of the middleportion of the permeate tube, and is radially offset inwardly away froman outer cylindrical surface of the hollow outlet portion of thepermeate tube.
 7. The filter of claim 6, wherein one or more leaves ofthe plurality of leaves of the filter element are attached to thepermeate tube through attachments between edges of the leaves and anouter cylindrical surface of an inlet portion of the permeate tubeadjacent to the first manifold, and wherein one or more leaves of theplurality of leaves of the filter element are attached to the permeatetube through attachments between edges of the leaves and an outercylindrical surface of an outlet portion of the permeate tube adjacentto the second manifold.
 8. The filter of claim 7, wherein theattachments do not comprise an adhesive.
 9. The filter of claim 7,wherein the attachments comprise a bond formed by ultrasonic welding,thermal bonding, IR bonding, radio frequency bonding, microwave bonding,laser welding, or hot air welding.
 10. The filter of claim 1, whereinone or more leaves of the plurality of leaves of the filter element areattached to the permeate tube through attachments between edges of theleaves and an outer cylindrical surface of the permeate tube.
 11. Thefilter of claim 10, wherein the attachments do not comprise an adhesive.12. The filter of claim 10, wherein the attachments comprise a bondformed by ultrasonic welding, thermal bonding, IR bonding, radiofrequency bonding, microwave bonding, laser welding, or hot air welding.13. The filter of claim 1, further comprising feed spacers positioned inbetween each of the plurality of leaves.
 14. The filter of claim 1,further comprising an inlet end cap attached to an inlet end of thepermeate tube, and an outlet end cap attached to an outlet end of thepermeate tube.
 15. The filter of claim 14, wherein the inlet end cap andthe outlet end cap are attached to the outer cylindrical shell and thepermeate tube with bonds that do not comprise an adhesive.
 16. Thefilter of claim 1, wherein each leaf of the plurality of leavescomprises a bond along at least a portion of an inlet edge and along atleast a portion of an outlet edge of the filter element, the bondsealing together adjacent pleats of the filter element to provide eachleaf with a fluid impervious seal at the inlet edge and the outlet edgeof the filter element.
 17. The filter of claim 16, wherein the bonds donot comprise an adhesive.
 18. The filter of claim 16, wherein the bondsare formed by ultrasonic welding, thermal bonding, IR bonding, radiofrequency bonding, microwave bonding, laser welding, or hot air welding.19. The filter of claim 1, wherein the plurality of leaves comprises aratio of leaf height to spiral diameter of less than or equal to
 3. 20.A spiral cross-flow filter, comprising: an outer shell; a permeate tubecoaxially aligned within the outer shell and radially offset therefrom,the permeate tube comprising: a blocked middle portion; a hollow inletportion comprising a first manifold formed by a perforated section of acylindrical wall of the inlet portion, wherein the perforated section isradially offset inwardly away from an outer cylindrical surface of theblocked middle portion of the permeate tube, and is radially offsetinwardly away from an outer cylindrical surface of the hollow inletportion of the permeate tube; and a hollow outlet portion comprising asecond manifold formed by a perforated section of a cylindrical wall ofthe outlet portion, wherein the perforated section is radially offsetinwardly away from an outer cylindrical surface of the blocked middleportion of the permeate tube, and is radially offset inwardly away froman outer cylindrical surface of the hollow outlet portion of thepermeate tube; and a pleated filter element comprising pleats locatedwithin an annulus between the outer shell and the permeate tube, thefilter element comprising a composite filter material comprising: afirst layer of a membrane material adjacent the outer shell; and asecond layer of a permeate spacer material adjacent the permeate tube,the pleats of the filter element defining a plurality ofcircumferentially spaced leaves, wherein the plurality of leaves wraparound the permeate tube in a uniform direction, wherein each leafcomprises an attachment to the permeate tube at a proximal edge of theleaf, and wherein each attachment comprises a direct bond between thepermeate tube and the membrane material.
 21. The filter of claim 20,wherein one or more leaves of the plurality of leaves of the filterelement are attached to the permeate tube through attachments betweenedges of the leaves and an outer cylindrical surface of the inletportion of the permeate tube adjacent to the first manifold, and whereinone or more leaves of the plurality of leaves of the filter element areattached to the permeate tube through attachments between edges of theleaves and an outer cylindrical surface of the outlet portion of thepermeate tube adjacent to the second manifold.
 22. The filter of claim21, wherein the attachments do not comprise an adhesive.
 23. The filterof claim 21, wherein the attachments comprise a bond formed byultrasonic welding, thermal bonding, IR bonding, radio frequencybonding, microwave bonding, laser welding, or hot air welding.
 24. Thefilter of claim 20, wherein each leaf of the plurality of leavescomprises a bond along at least a portion of an inlet edge and along atleast a portion of an outlet edge of the filter element, the bondsealing together adjacent pleats of the filter element to provide eachleaf with a fluid impervious seal at the inlet edge and the outlet edgeof the filter element.
 25. The filter of claim 24, wherein the bonds donot comprise an adhesive.
 26. The filter of claim 24, wherein the bondsare formed by ultrasonic welding, thermal bonding, IR bonding, radiofrequency bonding, microwave bonding, laser welding, or hot air welding.27. The filter of claim 20, wherein the plurality of leaves comprises aratio of leaf height to spiral diameter of less than or equal to 3.